Gas mileage info on '78 Buick Regal?

[Bill Johnston]

Hello,
I was wondering, is there anywhere (like a website) that would have the
gas mileage figures for an older car, to be specific a 1978 Buick
Regal? The owner's manual doesnt have it, neither does the Chilton's
book, and the govt. site doesn't have cars that old.

I ask this because I just stumbled on an old ad claiming that my car (a
1978 Buick Regal with a 3.8 liter 231cc V6) gets 27 mpg highway and 19
city. In practice, my car gets 20 hwy (with cruise, and driving like a
grandma) and 15 city- which I had figured must be normal for such an
old car. I have to wonder, is the ad inflating the figures, or is
something perhaps wrong with my car that's killing my gas mileage? (For
starters, the carb could probably use a rebuild). Given the $3 gas and
all, I'm really curious about this..

[Bela]

In rec.autos.antique Bill Johnston <***@yahoo.com> wrote:
BJ> Hello,
BJ> I was wondering, is there anywhere (like a website) that would have the
BJ> gas mileage figures for an older car, to be specific a 1978 Buick
BJ> Regal? The owner's manual doesnt have it, neither does the Chilton's
BJ> book, and the govt. site doesn't have cars that old.
BJ>
BJ> I ask this because I just stumbled on an old ad claiming that my car (a
BJ> 1978 Buick Regal with a 3.8 liter 231cc V6) gets 27 mpg highway and 19
BJ> city. In practice, my car gets 20 hwy (with cruise, and driving like a
BJ> grandma) and 15 city- which I had figured must be normal for such an
BJ> old car. I have to wonder, is the ad inflating the figures, or is
BJ> something perhaps wrong with my car that's killing my gas mileage? (For
BJ> starters, the carb could probably use a rebuild). Given the $3 gas and
BJ> all, I'm really curious about this..
BJ>

That ad was probably running in '78 or '77, and even then those figures should
have been taken with a block of salt. The 3800 is/was a great motor, but
after almost 30 years it ain't new. A thorough tune-up and/or minor repairs
might boost your mileage a little bit (or quite a bit if it's been totally
neglected) but expect no miracles. As they say, YMMV.

[Grumpy AuContraire]

Post by Bill Johnston
Hello,
I was wondering, is there anywhere (like a website) that would have the
gas mileage figures for an older car, to be specific a 1978 Buick
Regal? The owner's manual doesnt have it, neither does the Chilton's
book, and the govt. site doesn't have cars that old.
I ask this because I just stumbled on an old ad claiming that my car (a
1978 Buick Regal with a 3.8 liter 231cc V6) gets 27 mpg highway and 19
city. In practice, my car gets 20 hwy (with cruise, and driving like a
grandma) and 15 city- which I had figured must be normal for such an
old car. I have to wonder, is the ad inflating the figures, or is
something perhaps wrong with my car that's killing my gas mileage? (For
starters, the carb could probably use a rebuild). Given the $3 gas and
all, I'm really curious about this..

Cars of the 1970's were saddled with primitive emissions equipment that
resulted in poor gas mileage. Only by the mid 1980's did the mpg figures
improve.

As an aside, ignore the highly inflated EPA mileage figures for cars of
the era...

JT

[George Patterson]

Post by Bill Johnston
I ask this because I just stumbled on an old ad claiming that my car (a
1978 Buick Regal with a 3.8 liter 231cc V6) gets 27 mpg highway and 19
city.

Those would probably be EPA mileage figures. Back then, everybody joked about
them. People expected to get about 75% of the EPA figures.

One thing you can do to improve matters is to quit using cruise control. The
cruise control of that period was less efficient than the typical driver; it
would typically accelerate to just past the speed setting, back off on the
throttle until the speed dropped below it, then accelerate again. This
constantly works the accelerator pump on the carb. Today's fuel injection has
eliminated that problem.

George Patterson
Coffee is only a way of stealing time that should by rights belong to
your slightly older self.

[E***@gmail.com]

Post by Bill Johnston
I ask this because I just stumbled on an old ad claiming that my car (a
1978 Buick Regal with a 3.8 liter 231cc V6) gets 27 mpg highway and 19
city. In practice, my car gets 20 hwy (with cruise, and driving like a
grandma) and 15 city- which I had figured must be normal for such an
old car. I have to wonder, is the ad inflating the figures, or is
something perhaps wrong with my car that's killing my gas mileage? (For
starters, the carb could probably use a rebuild). Given the $3 gas and
all, I'm really curious about this..

The EPA figures in the ad may be a bit optimistic, but you ought to be
able to do better than 20 MPG on the highway. I knew someone who had a
Cutlass with the 3.8, a late '70s-early '80s car similar to yours, and
he said that he got very good mileage, although I no longer remember
the exact numbers and he would have been quoting Imperial MPG.

Unlike current cars, a non-feedback carbureted car can go out of
adjustment without any obvious signs like "Check Engine" lights. Also,
rear end ratios varied considerably more back then; you would get
better fuel economy with a 2.41:1 rear than a 3.23:1. I don't know what
range of rear ratios were available for your car/engine; the EPA figure
quoted in the ad will certainly be for the most economical--numerically
lowest--ratio.

I had a '79 Firebird with a 2-bbl 301 V8 that did 10-11 L/100 km on a
good day, which would be around 22 MPG. That car had a 2.41:1 rear
ratio. My '78 Trans Am with 400-4bbl can get 13 L/100 km on the
highway or a bit better, which is 18-19 MPG, and that's a big heavy car
with a big engine and 3.08:1 gears, and the smog stuff in place (except
for dual catalytic converters).

What can you do?
Check tire inflation
Tune up the engine--carb overhaul, check distributor spark advance
curves, new plugs, new air filter
Use lighter-weight engine oil and rear diff lube (presumably your
transmission is a TH-200 or TH-350; not much to be done there)
Check timing chain wear--your cam may be getting retarded due to chain
stretch
Check if your catalytic converter is plugged--the GM pellet-type
converters were pretty restrictive; a modern replacement converter will
flow much better
Check rear end gear ratio (easier if you can find the axle code
stamping)--change to a lower numerical ratio

[Ad absurdum per aspera]

Those are ideal figures for a carefully driven car in good tune. Note
also that in 1985 the EPA started adjusting their dynamometer-based
fuel economy figures in some way (I think with a sizeable fudge
factor) in response to widespread compaints that they were simplistic
tests that gave unrealistically high results. (Another major change
in the way the testing is done is now being discussed or perhaps it has
already been mandated, and is expected to ratchet the numbers down
again.)

Not until that platform got the redesigned "3800" version of the
engine (1988?) and consistent fitment of a 4-speed (1986-ish) would I
look for even an mpg or two increment on that, although driveability
and power doubtless improved. (I had some first experience with an '80
Cutlass Supreme with the V6 and distinctly recall it as being
labor-intensive to keep in tune, as well as finicky about gasoline.)


By today's standards it was a sizeable vehicle with a large aerodynamic
cross section, a fairly lossy tranny, and what a friend of mine refers
to as the heart-lung machine era of engine controls. Progress over
the fuel economy of earlier models was merely incremental until they
started building quite different cars with much better engine controls.


Note also that by now, the engine could be worn or the carb aging orout
of adjustment or the tranny slipping or whatnot -- additional factors
against getting the theoretical mileage potential.

Cheers,
--Joe